This invention relates to self-regulating horizontal deflection circuits with diode steering in which one of the diodes is biased.
Horizontal deflection circuits are used in conjunction with television picture tubes in television display devices. Typically, the horizontal deflection circuit includes a magnetic winding associated with the picture tube and a switching circuit by which energy from a dc voltage source is coupled to the winding and its associated reactances. The switching circuit is synchronized with synchronizing signals associated with the information content of the video to be displayed on the picture tube. In order to avoid distorted images on the displayed raster, the size of the horizontal scanning line and the peak deflection or scanning current must be maintained constant over substantial periods of time.
Many conditions can cause the size of the horizontal scanning line to vary. If the direct energizing voltage for the horizontal deflection circuit varies, the scanning energy and hence the width of the horizontal scanning line may vary. It has in the past been customary to regulate the direct voltage applied to the horizontal deflection circuit by the use of a dissipative regulator. Requirements for low power consumption in television receivers is reducing the use of such dissipative regulators in favor of nondissipative types.
Another approach to regulating the scan width involves the use of a self-regulating deflection circuit, such as is described in the article "A New Horizontal Output Deflection Circuit" by Peter L. Wessel, which appeared in the IEEE Transactions on Broadcast and Television Receivers, August, 1972, Vol. BTR-18, No. 3, pages 117-182. The Wessel deflection circuit may be energized from an unregulated direct voltage, and uses a single switching transistor to perform the switching function for the horizontal deflection and for nondissipative switching regulation. In the Wessel circuit, the unregulated direct voltage is applied across the primary winding of a transformer by the switching transistor. The deflection winding, retrace capacitor and damper diode associated with the horizontal deflection are coupled across the collector-emitter path of the switching transistor by a first diode poled for conduction in the same direction as the collector-emitter path. A secondary winding of the transformer is coupled across the deflection winding by a second diode poled to conduct and transfer energy from the primary to the deflection winding during the retrace interval. It is desirable to eliminate the secondary winding, and thereby reduce the total number of windings.
A horizontal deflection circuit in which the secondary winding is eliminated is described in U.S. Pat. No. 3,906,307 issued Sept. 16, 1975 in the name of J. Van Hattum. However, in the Van Hattum arrangement, an additional inductor and capacitor are used. The necessity for the additional inductor negates the advantage of elimination of the secondary winding.